The Imamiyya agree that whoever denies the Imamate of one of the Imams and rejects what Allah تعالى has obligated him of the imperative of obedience, then he is a kafir, astray, deserving of eternity in the Fire.

And the Mu`tazila concur in opposition to that and deny the kufr of who we have mentioned, and judge fisq for some of them exclusively and what is apart from fisq of disobedience for some of them.